While the hypothalamo-pituitary-adrenal axis (HPA) activates a general stress response by increasing glucocorticoid (Gc) synthesis, biological stress resulting from infections triggers the ...inflammatory response through production of cytokines. The pituitary gland integrates some of these signals by responding to the pro-inflammatory cytokines IL6 and LIF and to a negative Gc feedback loop. The present work used whole-genome approaches to define the LIF/STAT3 regulatory network and to delineate cross-talk between this pathway and Gc action. Genome-wide ChIP-chip identified 3,449 STAT3 binding sites, whereas 2,396 genes regulated by LIF and/or Gc were found by expression profiling. Surprisingly, LIF on its own changed expression of only 85 genes but the joint action of LIF and Gc potentiated the expression of more than a thousand genes. Accordingly, activation of both LIF and Gc pathways also potentiated STAT3 and GR recruitment to many STAT3 targets. Our analyses revealed an unexpected gene cluster that requires both stimuli for delayed activation; 83% of the genes in this cluster are involved in different cell defense mechanisms. Thus, stressors that trigger both general stress and inflammatory responses lead to activation of a stereotypic innate cellular defense response.
Context:
Cushing disease (CD) is due to pituitary corticotrope adenomas that produce unrestrained ACTH secretion and have lost the negative feedback exerted by glucocorticoids (GCs). GCs also ...restrain corticotrope proliferation, and the mechanisms of this inhibition are poorly understood.
Objective:
The aim of the study was to identify cell cycle regulatory genes that are regulated by GCs and the glucocorticoid receptor and to assess regulatory genes that have a rate-limiting action on corticotrope proliferation and may be disregulated in CD.
Design:
The mouse corticotrope tumor cells AtT-20 were used to identify GC-regulated genes that contribute to control of cell cycle progression. Surgery sections from patients with CD were used to assess expression of CABLES1 in corticotrope adenomas.
Methods:
Gene expression profiling, small interfering RNA knockdowns, cell cycle analyses, and genetic manipulations were performed in AtT-20 cells. Sequencing of chromatin immunoprecipitation for pituitary-restricted transcription factors and RNA polymerase II were used to identify regulatory elements and genes that bind GR and are direct transcriptional targets. A panel of previously well-characterized corticotrope adenomas was used to correlate expression of CABLES1 with that of other markers.
Results:
GCs altered expression of 3 positive and 3 negative regulators of cell cycle progression. Two Myc genes (L-Myc and N-Myc) and E2F2 are repressed by GCs, whereas genes for the negative regulators of the cell cycle, Gadd45β, Gadd45γ, and Cables1 are activated by GCs. Cables1 small interfering RNA knockdown strongly stimulates AtT-20 cell proliferation and antagonizes the growth inhibition produced by GCs. The Gadd45 and Cables1 genes have the hallmarks of direct GC targets. CABLES1 is expressed in normal human pituitary cells, but expression is lost in ∼55% of corticotrope adenomas, and this is strongly correlated with the loss of p27Kip1 expression.
Conclusions:
CABLES1 is a critical regulator of corticotrope proliferation that defines a pathway often inactivated in CD and links proliferation to GC resistance.
DAVID syndrome is a rare condition combining anterior pituitary hormone deficiency with common variable immunodeficiency. NFKB2 mutations have recently been identified in patients with ACTH and ...variable immunodeficiency. A similar mutation was previously found in Nfkb2 in the immunodeficient Lym1 mouse strain, but the effect of the mutation on endocrine function was not evaluated.
We ascertained six unrelated DAVID syndrome families. We performed whole exome and traditional Sanger sequencing to search for causal genes. Lym1 mice were examined for endocrine developmental anomalies.
Mutations in the NFKB2 gene were identified in three of our families through whole exome sequencing, and in a fourth by direct Sanger sequencing. De novo origin of the mutations could be demonstrated in three of the families. All mutations lie near the C-terminus of the protein-coding region, near signals required for processing of NFΚB2 protein by the alternative pathway. Two of the probands had anatomical pituitary anomalies, and one had growth and thyroid hormone as well as ACTH deficiency; these findings have not been previously reported. Two children of one of the probands carried the mutation and have to date exhibited only an immune phenotype. No mutations were found near the C-terminus of NFKB2 in the remaining two probands; whole exome sequencing has been performed for one of these. Lym1 mice, carrying a similar Nfkb2 C-terminal mutation, showed normal pituitary anatomy and expression of proopiomelanocortin (POMC).
We confirm previous findings that mutations near the C-terminus of NFKB2 cause combined endocrine and immunodeficiencies. De novo status of the mutations was confirmed in all cases for which both parents were available. The mutations are consistent with a dominant gain-of-function effect, generating an unprocessed NFKB2 super-repressor protein. We expand the potential phenotype of such NFKB2 mutations to include additional pituitary hormone deficiencies as well as anatomical pituitary anomalies. The lack of an observable endocrine phenotype in Lym1 mice suggests that the endocrine component of DAVID syndrome is either not due to a direct role of NFKB pathways on pituitary development, or else that human and mouse pituitary development differ in its requirements for NFKB pathway function.
Context: Tpit is a T-box transcription factor important for terminal differentiation of pituitary proopiomelanocortin-expressing cells. We previously showed that human and murine mutations in the ...gene encoding this highly cortico/melanotrope-specific transcription factor cause a neonatal onset form of congenital isolated ACTH deficiency (IAD). We characterized the largest series of neonatal IAD patients caused by TPIT mutations, and this revealed a highly homogeneous clinical presentation. So far, 12 different loss-of-function TPIT mutations have been identified. The methionine 86 arginine (M86R) TPIT mutation was recently identified in compound heterozygosity with the 782delA frame-shift mutation in two siblings with early-onset IAD.
Objective: We conducted a functional analysis of the missense M86R mutation to assess transcriptional activity, DNA binding activity, and nuclear location, as well as protein-protein interactions.
Results: Although the M86 residue is located within the T-box DNA-binding domain, it did not affect monomer DNA-binding activity per se, but it impaired DNA binding with other DNA-bound proteins, including itself (homodimers) and pituitary homeobox 1 (Pitx1). The M86 residue is at the interface between T domains in the T dimers crystal structure, and it appears that the same residue is involved in heterodimer formation with pituitary Pitx1. Furthermore, TPIT M86R is deficient in the recruitment of the coactivator SRC2 that partly mediates the CRH stimulation of proopiomelanocortin transcription.
Conclusion: Thus, the M86R TPIT mutation is defining an important surface of the T domain for multiple protein interactions and for transcription.
In efforts to define mechanisms of transcriptional activation by the orphan nuclear receptor NGFI-B (Nur77), we identified TIF1 beta by mass spectrometry within a nuclear protein complex containing ...NGFI-B. TIF1 beta , also known as KAP-1 (KRAB domain-associated protein) or KRIP-1, acts as a transcriptional corepressor for many transcription factors, in particular for the Krueppel-associated box domain-containing zinc finger transcription factors. TIF1 beta is also an intrinsic component of two chromatin remodeling and histone deacetylase complexes, the N-CoR1 and nucleosome remodeling and deacetylation complexes. In contrast to these activities, we report that TIF1 beta is a coactivator of NGFI-B and that it is as potent as the SRC coactivators in this context. Using pull-down assays and immunoprecipitation, we showed that TIF1 beta interacts directly with NGFI-B and with other Nur family members. NGFI-B is an important mediator of hypothalamic corticotropin-releasing hormone (CRH) activation of proopiomelanocortin (POMC) transcription, and TIF1 beta enhances transcription mediated through the NGFI-B target, the Nur response element (NurRE). The NurRE binds Nur factor dimers and is responsive to signaling pathways. In keeping with the role of NGFI-B as mediator of CRH signaling, we found that TIF1 beta is recruited to the POMC promoter following CRH stimulation and that TIF1 beta potentiates CRH and protein kinase A signaling through the NurRE; it acts synergistically with the SRC2 coactivator. However, the actions of TIF1 beta and SRC2 were mapped to different NGFI-B AF-1 subdomains. Taken together, these results indicate that TIF1 beta is an important coactivator of NGFI-B- dependent transcription.
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